(12) United States Patent
`Zeira et al.
`
`USOO6728292B2
`(10) Patent No.:
`US 6,728,292 B2
`45) Date of Patent:
`Apr. 27, 2004
`
`9
`
`(54) COMBINED CLOSED LOOP/OPEN LOOP
`POWER CONTROL IN A TIME DIVISION
`DUPLEX COMMUNICATION SYSTEM
`(75) Inventors: Ariela Zeira, Huntington, NY (US);
`Faith M. Ozluturk, Port Washington,
`NY (US); Sung-Hyuk Shin, Fort Lee,
`NJ (US)
`(73) Assignee: InterDigital Technology Corporation,
`Wilmington, DE (US)
`
`(*) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`This patent is Subject to a terminal dis-
`claimer.
`
`EP
`EP
`EP
`EP
`WO
`WO
`
`1/2001 Lomp
`6,175,586 B1
`CISCE 58: Engyet al.
`6,373.823 B1
`4/2002 Chen et al.
`6,449.462 B1
`9/2002 Gunnersson et al.
`6,600,772 B1 * 7/2003 Zeira et al. ................. 375/130
`FOREIGN PATENT DOCUMENTS
`O462952
`12/1991
`O610030
`8/1994
`O682419
`11/1995
`OSOO689
`4/1998
`97.491.97
`12/1997
`9845962
`10/1998
`OTHER PUBLICATIONS
`“Specification of Air-Interface for the 3G Mobile System”,
`Version 1.0, ARIB, Jan. 14, 1999.
`“Combined Closed-Loop/Open-Loop Power Control Pro
`cess for Time Division Duplexing”, Ariela Zeira, Sung-Huk
`Shin and Faith Ozluturk, Apr. 1999.
`“Performance of Weighted Open Loop Scheme for Uplink
`21 Ap1. No.: 10,459,035
`(21) App
`/459,
`Power Control in TDD Mode”, Ariela Zeira and Sung-Hyuk
`Shin, May 1999.
`(22) Filed:
`Jun. 11, 2003
`“Text Proposal for S1.24”, Ariela Zeira, Sung-Hyuk Shin
`O
`O
`and Stephen Dick, May 1999.
`(65)
`Prior Publication Data
`* cited by examiner
`US 2003/0198279 A1 Oct. 23, 2003
`Primary Examiner Temesghen Ghebretinsae
`Related U.S. Application Data
`(74) Attorney, Agent, or Firm Volpe and Koenig, P.C.
`(63) Continuation of application No. 09/531,359, filed on Mar.
`(57)
`ABSTRACT
`21, 2000, now Pat. No. 6,600,772.
`Aspread spectrum time division duplex user equipment uses
`(51) Int. Cl. ............................ H04B 1/69; H04B 1/707
`frames having time slots for communication. The user
`(52) U.S. Cl. ....................... 375/130; 375/295; 455/522;
`equipment receives power commands and a first communi
`370/342
`cation having a transmission power level in a first time slot.
`(58) Field of Search ................................. 375/130, 295
`375/140; 455/522, 69; 370/3 43 253 A power level of the first communication is measured as
`s
`s s/ - 9
`s
`received. A pathloSS estimate is determined based on in part
`References Cited
`the measured received first communication power level and
`the first communication transmission power level. A trans
`mission power level for the Second communication in a
`Second time slot form the user equipment is set based on in
`part the pathloSS estimate weighted by a quality factor
`adjusted by the power command. The quality factor
`decreases as a number of time slots between the first and
`Second time slots increases.
`
`(56)
`
`U.S. PATENT DOCUMENTS
`4,868,795. A
`9/1989 McDavid et al.
`5,056,109 A 10/1991 Gilhousen et al.
`5,542,111 A 7/1996 Ivanov et al.
`5,839,056 A 11/1998 Hakkinen
`5,859,838 A
`1/1999 Soliman
`6,101,179 A
`8/2000 Soliman
`6,108,561 A
`8/2000 Mallinckrodt
`
`8 Claims, 7 Drawing Sheets
`
`ERAE APOWER CONTROL cottai
`BASED ON A SIGNALONTERFERENCE
`RAT OF ACMAUNCAONSENT
`FROM HE TRANSTTNG STAN
`
`RANSMTA DEUNATIN ANTHE POER
`COMMAND FROE RECEIWINSTATION
`
`DEERMINE THE RECEIVE POWER LEVEL
`OF THE RERUNICATION FROM THE
`RECENING STATIONAE
`TRANSTING STATION
`
`-40
`
`L/ 42
`
`ETERINE ANSTMAEFALS3BETEEN
`The RECEIWN ANDTRANSTING STAONBY
`8BTRACTNS HERECEWEC&MNCATON's
`WEREWELN 3 FROM THE COMMUNICATON'S
`TRANSASSION PREVELN ds
`
`ALTY OF THE
`DETERIN THE
`8TA
`PATH 888
`
`46
`
`STN HE TRANSRITTN38TATN's POWER
`LEVEL BASE ONNPART The POER
`COMAN AN WEEIN THE ESATE
`Athloss BASED ON THE ESTMATE's QUALITY
`
`Ericsson Exhibit 1004
`Page 1
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`

`

`U.S. Patent
`
`Apr. 27, 2004
`
`Sheet 1 of 7
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`US 6,728,292 B2
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`
`
`Ericsson Exhibit 1004
`Page 2
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`

`

`U.S. Patent
`
`Apr. 27, 2004
`
`Sheet 2 of 7
`
`US 6,728,292 B2
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`
`
`s
`CO
`Co
`
`Co
`Cy)
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`re
`Co
`Cy
`
`Ericsson Exhibit 1004
`Page 3
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`

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`U.S. Patent
`
`Apr. 27, 2004
`
`Sheet 3 of 7
`
`US 6,728,292 B2
`
`FIG, 3
`
`GENERATE A POWER CONTROL COMMAND
`BASED ON A SIGNAL TO INTERFERENCE
`RATO OF A COMMUNICATIONSENT
`FROM THE TRANSMITTING STATION
`
`TRANSMIT A COMMUNICATION AND THE POWER
`COMMAND FROM THE RECEIVING STATION
`
`DETERMINE THE RECEIVED POWER LEVEL
`OF THE COMMUNICATION FROM THE
`RECEIVING STATION AT THE
`TRANSMITTING STATION
`
`DETERMINE AN ESTMATED PATH LOSS BETWEEN
`THE RECEIVING AND TRANSMITTING STATION BY
`SUBTRACTING THE RECEIVED COMMUNICATION'S
`POWER LEVEL N dB FROM THE COMMUNICATION'S
`TRANSMISSION POWER LEVEL IN dB
`
`DETERMINE THE QUALITY OF THE
`ESTMATED PATH LOSS
`
`SETTING THE TRANSMITTING STATION'S POWER
`LEVEL BASED ON IN PART THE POWER
`COMMAND AND WEIGHTING THE ESTMATED
`PATH LOSS BASED ON THE ESTMATES QUALITY
`
`
`
`
`
`38
`
`40
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`42
`
`44
`
`46
`
`48
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`Ericsson Exhibit 1004
`Page 4
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`U.S. Patent
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`Apr. 27, 2004
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`Sheet 4 of 7
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`US 6,728,292 B2
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`Ericsson Exhibit 1004
`Page 5
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`Ericsson Exhibit 1004
`Page 5
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`U.S. Patent
`
`Apr. 27, 2004
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`Sheet 5 of 7
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`US 6,728,292 B2
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`FIG, 5
`
`i
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`
`DELAY (SLOT)
`
`Ericsson Exhibit 1004
`Page 6
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`U.S. Patent
`
`Apr. 27, 2004
`
`Sheet 6 of 7
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`US 6,728,292 B2
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`FIG, 7
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`
`Ericsson Exhibit 1004
`Page 7
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`U.S. Patent
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`Apr. 27, 2004
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`Sheet 7 of 7
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`US 6,728,292 B2
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`FIG, 9
`
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`
`Ericsson Exhibit 1004
`Page 8
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`

`

`1
`COMBINED CLOSED LOOP/OPEN LOOP
`POWER CONTROL IN A TIME DIVISION
`DUPLEX COMMUNICATION SYSTEM
`CROSS REFERENCE TO RELATED
`APPLICATION
`This application is a continuation of U.S. patent applica
`tion Ser. No. 09/531,359 filed Mar. 21, 2000, which is
`incorporated by reference as if fully set forth.
`BACKGROUND
`This invention generally relates to Spread Spectrum time
`division duplex (TDD) communication systems. More
`particularly, the present invention relates to a System and
`method for controlling transmission power within TDD
`communication Systems.
`FIG. 1 depicts a wireleSS spread Spectrum time division
`duplex (TDD) communication system. The system has a
`plurality of base stations 301-307. Each base station 301
`communicates with user equipments (UES) 321-323 in its
`operating area. Communications transmitted from a base
`station 301 to a UE 321 are referred to as downlink com
`munications and communications transmitted from a UE
`321 to a base station 301 are referred to as uplink commu
`nications.
`25
`In addition to communicating over different frequency
`Spectrums, spread Spectrum TDD Systems carry multiple
`communications over the same spectrum. The multiple
`Signals are distinguished by their respective chip code
`Sequences (codes). Also, to more efficiently use the spread
`Spectrum, TDD Systems as illustrated in FIG. 2 use repeating
`frames 34 divided into a number of time slots 361-36n, Such
`as fifteen time slots. In Such systems, a communication is
`sent in selected time slots 361-36n using selected codes.
`Accordingly, one frame 34 is capable of carrying multiple
`communications distinguished by both time slot 361-36n
`and code. The combination of a single code in a single time
`slot is referred to as a resource unit. Based on the bandwidth
`required to Support a communication, one or multiple
`resource units are assigned to that communication.
`Most TDD systems adaptively control transmission
`power levels. In a TDD System, many communications may
`share the same time slot and spectrum. When a UE 321 or
`base Station 301 is receiving a Specific communication, all
`the other communications using the same time slot and
`Spectrum cause interference to the Specific communication.
`Increasing the transmission power level of one communi
`cation degrades the Signal quality of all other communica
`tions within that time slot and spectrum. However, reducing
`the transmission power level too far results in undesirable
`signal to noise ratios (SNRs) and bit error rates (BERs) at the
`receivers. To maintain both the Signal quality of communi
`cations and low transmission power levels, transmission
`power control is used.
`One approach to control transmission power levels is
`open loop power control. In open loop power control,
`typically a base station 301 transmits to a UE321 a reference
`downlink communication and the transmission power level
`of that communication. The UE 321 receives the reference
`communication and measures its received power level. By
`Subtracting the received power level from the transmission
`power level, a pathloSS for the reference communication is
`determined. To determine a transmission power level for the
`uplink, the downlink pathloSS is added to a desired received
`power level at the base station 301. The UE's transmission
`power level is Set to the determined uplink transmission
`power level.
`
`2
`Another approach to control transmission power level is
`closed loop power control. In closed loop power control,
`typically the base station 301 determines the signal to
`interference ratio (SIR) of a communication received from
`the UE321. The determined SIR is compared to a target SIR
`(SIRTARGET). Based on the comparison, the base station
`301 transmits a power command, bTPC. After receiving the
`power command, the UE 321 increases or decreases its
`transmission power level based on the received power
`command.
`Both closed loop and open loop power control have
`disadvantages. Under certain conditions, the performance of
`closed loop Systems degrades. For instance, if communica
`tions Sent between a UE and a base Station are in a highly
`dynamic environment, Such as due to the UE moving, Such
`Systems may not be able to adapt fast enough to compensate
`for the changes. The update rate of closed loop power
`control in TDD is 100 cycles per second which is not
`Sufficient for fast fading channels. Open loop power control
`is Sensitive to uncertainties in the uplink and downlink gain
`chains and interference levels.
`One approach to combining closed loop and open loop
`power control was proposed by the ASSociation of Radio
`Industries and Business (ARIB) and uses Equations 1, 2, and
`3.
`
`TUE = PBS (n) + L
`
`PBS (n) = PBS (n - 1) + b TPCATPC
`
`1: if SIRBs (SIRTARGET
`- 1: if SIRBs),SIRTARGET
`
`Equation 1
`
`Equation 2
`
`Equation 3
`
`T is the determined transmission power level of the UE
`32. L is the estimated downlink pathloss. Ps(n) is the
`desired received power level of the base station 30 as
`adjusted by Equation 2. For each received power command,
`be, the desired received power level is increased or
`decreased by A. A., is typically one decibel (dB). The
`power command, b, is one, when the SIR of the UES
`uplink communication as measured at the base Station 30,
`SIRs, is less than a target SIR, SIRA. Conversely, the
`power command is minus one, when SIRs is larger than
`SIRTARGET.
`Under certain conditions, the performance of these Sys
`tems degrades. For instance, if communications Sent
`between a UE 32 and a base station 30 are in a highly
`dynamic environment, Such as due to the UE32 moving, the
`path loSS estimate for open loop Severely degrades the
`overall System's performance. Accordingly, there is a need
`for alternate approaches to maintain Signal quality and low
`transmission power levels for all environments and Sce
`narios.
`
`SUMMARY
`Combined closed loop/open loop power control controls
`transmission power levels in a spread spectrum time division
`duplex communication Station. A first communication Sta
`tion receives communications from a Second communica
`tion Station. The first Station transmits power commands
`based on in part a reception quality of the received com
`munications. The first Station transmits a Second communi
`cation having a transmission power level in a first time slot.
`The Second Station receives the Second communication and
`the power commands. A power level of the Second commu
`nication as received is measured. A path loSS estimate is
`
`US 6,728,292 B2
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`3
`determined based on in part the measured received Second
`communication power level and the first communication
`transmission power level. The Second Station transmits a
`Second communication to the first Station in a Second time
`slot. The Second communication transmission power level is
`Set based on in part the path loSS estimate weighted by a
`factor and the power commands. The factor is a function of
`a time Separation of the first and Second time slots.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 illustrates a prior art TDD system.
`FIG. 2 illustrates time slots in repeating frames of a TDD
`System.
`FIG. 3 is a flow chart of combined closed loop/open loop
`power control.
`FIG. 4 is a diagram of components of two communication
`Stations using combined closed loop/open loop power con
`trol.
`FIGS. 5-10 depict graphs of the performance of a closed
`loop, ARIB’s proposal and two (2) schemes of combined
`closed loop/open loop power control.
`
`15
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`The preferred embodiments will be described with refer
`ence to the drawing figures where like numerals represent
`like elements throughout. Combined closed loop/open loop
`power control will be explained using the flow chart of FIG.
`3 and the components of two simplified communication
`stations 50, 52 as shown in FIG. 4. For the following
`discussion, the communication Station having its transmit
`ter's power controlled is referred to as the transmitting
`Station 52 and the communication Station receiving power
`controlled communications is referred to as the receiving
`station 50. Since combined closed loop/open loop power
`control may be used for uplink, downlink or both types of
`communications, the transmitter having its power controlled
`may be located at a base station 30, UE 32 or both.
`Accordingly, if both uplink and downlink power control are
`used, the receiving and transmitting Station's components
`are located at both the base station 30, and UE 32.
`The receiving station 50 receives various radio frequency
`Signals including communications from the transmitting
`Station 52 using an antenna 56, or alternately, an antenna
`array. The received signals are passed through an isolator 60
`to a demodulator 68 to produce a baseband signal. The
`baseband Signal is processed, Such as by a channel estima
`tion device 96 and a data estimation device 98, in the time
`Slots and with the appropriate codes assigned to the trans
`mitting Station's communication. The channel estimation
`device 96 commonly uses the training Sequence component
`in the baseband Signal to provide channel information, Such
`as channel impulse responses. The channel information is
`used by the data estimation device 98, the interference
`measurement device 90, the Signal power measurement
`device 92 and the transmit power calculation device 94. The
`data estimation device 98 recovers data from the channel by
`estimating Soft Symbols using the channel information.
`Using the Soft Symbols and channel information, the trans
`mit power calculation device 94 controls the receiving
`Station's transmission power level by controlling the gain of
`an amplifier 76.
`The Signal power measurement device 92 uses either the
`soft symbols or the channel information, or both, to deter
`mine the received signal power of the communication in
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`4
`decibels (dB). The interference measurement device 90
`determines the interference level in dB, Is, within the
`channel, based on either the channel information, or the Soft
`symbols generated by the data estimation device 98, or both.
`The closed loop power command generator 88 uses the
`measured communication's received power level and the
`interference level, Is, to determine the Signal to Interfer
`ence Ratio (SIR) of the received communication. Based on
`a comparison of the determined SIR with a target SIR
`(SIR), a closed loop power command is generated,
`bre, Such as a power command bit, bec, Step 38.
`Alternately, the power command may be based on any
`quality measurement of the received signal.
`For use in estimating the path loSS between the receiving
`and transmitting Stations 50, 52 and Sending data, the
`receiving Station 50 sends a communication to the transmit
`ting station 58, step 40. The communication may be sent on
`any one of various channels. Typically, in a TDD System, the
`channels used for estimating path loSS are referred to as
`reference channels, although other channels may be used. If
`the receiving station 50 is a base station 30, the commu
`nication is preferably Sent over a downlink common channel
`or a common control physical channel (CCPCH). Data to be
`communicated to the transmitting Station 52 over the refer
`ence channel is referred to as reference channel data. The
`reference data may include, as shown, the interference level,
`Is, multiplexed with other reference data, Such as the
`transmission power level of the reference channel, Ts. The
`interference level, Is, and reference channel power level,
`Ts, may be sent in other channels, Such as a signaling
`channel. The closed loop power control command, b, is
`typically Sent in a dedicated channel. The dedicated channel
`is dedicated to the communication between the receiving
`station 50 and transmitting station 52, step 40.
`The reference channel data is generated by a reference
`channel data generator 86. The reference data is assigned
`one or multiple resource units based on the communication's
`bandwidth requirements. A spreading and training Sequence
`insertion device 82 Spreads the reference channel data and
`makes the spread reference data time-multiplexed with a
`training Sequence in the appropriate time slots and codes of
`the assigned resource units. The resulting Sequence is
`referred to as a communication burst. The communication
`burst is subsequently amplified by an amplifier 78. The
`amplified communication burst may be Summed by a Sum
`device 72 with any other communication burst created
`through devices, Such as a data generator 84, spreading and
`training sequence insertion device 80 and amplifier 76.
`The Summed communication bursts are modulated by a
`modulator 64. The modulated Signal is passed through an
`isolator 60 and radiated by an antenna 56 as shown or,
`alternately, through an antenna array. The radiated Signal is
`passed through a wireless radio channel 54 to an antenna 58
`of the transmitting station 52. The type of modulation used
`for the transmitted communication can be any of the those
`known to those skilled in the art, Such as direct phase shift
`keying (DPSK) or quadrature phase shift keying (QPSK).
`The antenna 58 or, alternately, antenna array of the
`transmitting Station 52 receives various radio frequency
`Signals. The received signals are passed through an isolator
`62 to a demodulator 66 to produce a baseband signal. The
`baseband Signal is processed, Such as by a channel estima
`tion device 100 and a data estimation device 102, in the time
`Slots and with the appropriate codes assigned to the com
`munication burst of the receiving station 50. The channel
`estimation device 100 commonly uses the training Sequence
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`S
`component in the baseband Signal to provide channel
`information, Such as channel impulse responses. The chan
`nel information is used by the data estimation device 102, a
`power measurement device 110 and a quality measurement
`device 114.
`The power level of the processed communication corre
`sponding to the reference channel, Rus, is measured by the
`power measurement device 110 and Sent to a pathloSS
`estimation device 112, step 42. Both the channel estimation
`device 100 and the data estimation device 102 are capable of
`Separating the reference channel from all other channels. If
`an automatic gain control device or amplifier is used for
`processing the received signals, the measured power level is
`adjusted to correct for the gain of these devices at either the
`power measurement device 110 or the pathloSS estimation
`15
`device 112. The power measurement device 110 is a com
`ponent of the combined closed loop/open loop controller
`108. As illustrated in FIG. 4, the combined closed loop/open
`loop power controller 108 comprises the power measure
`ment device 110, pathloss estimation device 112, quality
`measurement device 114, and transmit power calculation
`device 116.
`To determine the path loSS, L, the transmitting Station 52
`also requires the communication's transmitted power level,
`Ts. The transmitted power level, Ts, may be sent along
`with the communication's data or in a Signaling channel. If
`the power level, Tes, is sent along with the communications
`data, the data estimation device 102 interprets the power
`level and Sends the interpreted power level to the pathloSS
`estimation device 112. If the receiving station 50 is a base
`Station 30, preferably the transmitted power level, Ts, is
`sent via the broadcast channel (BCH) from the base station
`30. By Subtracting the received communication's power
`level, Rs in dB, from the sent communication's transmitted
`power level, Ts in dB, the pathloSS estimation device 112
`estimates the path loss, L, between the two stations 50, 52,
`Step 44. In certain situations, instead of transmitting the
`transmitted power level, Ts, the receiving Station 50 may
`transmit a reference for the transmitted power level. In that
`case, the pathloSS estimation device 112 provides reference
`levels for the path loss, L.
`If a time delay exists between the estimated path loSS and
`the transmitted communication, the path loSS experienced by
`the transmitted communication may differ from the calcu
`lated loSS. In TDD Systems where communications are sent
`in differing time slots 361-36, the time slot delay between
`received and transmitted communications may degrade the
`performance of an open loop power control System. Com
`bined closed loop/open loop power control utilizes both
`closed loop and open loop power control aspects. If the
`quality of the path loSS measurement is high, the System
`primarily acts as an open loop System. If the quality of the
`path loSS measurement is low, the System primarily acts as
`a closed loop System. To combine the two power control
`aspects, the System weights the open loop aspect based on
`the quality of the path loSS measurement.
`A quality measurement device 114 in a weighted open
`loop power controller 108 determines the quality of the
`estimated path loSS, Step 46. The quality may be determined
`using the channel information generated by the channel
`estimation device 100, the soft symbols generated by the
`data estimation device 102 or other quality measurement
`techniques. The estimated path loSS quality is used to weight
`the path loSS estimate by the transmit power calculation
`device 116. If the power command, b, was Sent in the
`communication's data, the data estimation device 102 inter
`prets the closed loop power command, br. Using the
`
`6
`closed loop power command, b, and the weighted path
`loSS, the transmit power calculation device 116 Sets the
`transmit power level of the receiving station 50, step 48.
`The following is one of the preferred combined closed
`loop/open loop power control algorithms. The transmitting
`Station's power level in decibels, Ps, is determined using
`Equations 4 and 6.
`
`Pts=P+G(n)+CL
`Equation 4
`P is the power level that the receiving station 50 desires
`to receive the transmitting Station's communication in dB.
`P is determined by the desired SIR at the receiving station
`50, SIRA, and the interference level, Is, at the receiv
`ing Station 50 using Equation 5.
`
`PoSIRAETH's
`Equation 5
`Is is either Signaled or broadcasted from the receiving
`station 50 to the transmitting station 52. For downlink power
`control, SIR
`is known at the transmitting Station 52.
`For uplink power control, SIRA
`is signaled from the
`receiving station 50 to the transmitting station 52. G(n) is the
`closed loop power control factor. Equation 6 is one equation
`for determining G(n).
`
`G(n-1) is the previous closed loop power control factor.
`The power command, be, for use in Equation 6 is either
`+1 or -1. One technique for determining the power
`command, bec, is Equation 3. The power command, bre,
`is typically updated at a rate of 100 ms in a TDD system,
`although other update rates may be used. AP, is the change
`in power level. The change in power level is typically 1 dB
`although other values may be used. As a result, the closed
`loop factor increases by 1 dB if b
`is +1 and decreases by
`1 dB if b
`is -1.
`The weighting value, C, is determined by the quality
`measurement device 114. C. is a measure of the quality of the
`estimated path loSS and is, preferably, based on the number
`of time slots, D, between the time slot of the last path loss
`estimate and the first time slot of the communication trans
`mitted by the transmitting station 52. The value of C. is from
`Zero to one. Generally, if the time difference, D, between the
`time slots is Small, the recent path loSS estimate will be fairly
`accurate and C. is Set at a value close to one. By contrast, if
`the time difference is large, the path loSS estimate may not
`be accurate and the closed loop aspect is most likely more
`accurate. Accordingly, C. is Set at a value closer to Zero.
`Equations 7 and 8 are two equations for determining C,
`although others may be used.
`
`C=1-(D-1)/(D-1)
`
`Equation 7
`
`Equation 8
`C=max{1-(D-1)/(Date-1), 0}
`is the maximum possible delay. A typical value for a
`D,
`frame having fifteen time slots is Seven. If the delay is D.,
`C. is Zero. D,
`is the maximum allowed time slot
`delay for using open loop power control. If the delay
`exceeds D, open loop power control is effectively
`turned off by Setting C=0. Using the calculated transmit
`power level, Ps, determined by a transmit power calcula
`tion device 116, the combined closed loop/open loop power
`controller 108 sets the transmit power of the transmitted
`communication.
`Data to be transmitted in a communication from the
`transmitting Station 52 is produced by a data generator 106.
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`7
`The communication data is spread and time-multiplexed
`with a training Sequence by the spreading and training
`Sequence insertion device 104 in the appropriate time slots
`and codes of the assigned resource units producing a com
`munication burst. The spread signal is amplified by the
`amplifier 74 and modulated by the modulator 70 to radio
`frequency.
`The combined closed loop/open loop power controller
`108 controls the gain of the amplifier 74 to achieve the
`determined transmit power level, Ps, for the communica
`tion. The power controlled communication is passed through
`the isolator 62 and radiated by the antenna 58.
`Equations 9 and 10 are another preferred combined closed
`loop/open loop power control algorithm.
`
`8
`Graphs 122, 124 depict the results for an O. set at 0.5. As
`shown, for all delayS eXcluding the maximum, Schemes I
`and II outperform closed loop power control. The ARIB
`proposal only outperforms the others at the lowest delay
`(D=1).
`Graphs 126, 128 depict the results for an C. set using
`Equation 7 with D,
`equal to Seven. AS Shown, Schemes I
`and II outperform both closed loop and the ARIB proposal
`at all delays, D.
`What is claimed is:
`1. A spread Spectrum time division dupleX user
`equipment, the user equipment using frames with time slots
`for communication, receiving power commands and receiv
`ing a first communication having a transmission power level
`in a first time slot, measuring a power level of the first
`communication as received and determining a pathloSS
`estimate based on in part the measured received first com
`munication power level and the first communication trans
`mission power level, the user equipment comprising:
`means for Setting a transmission power level for a Second
`communication in a Second time slot from the user
`equipment based on in part the pathloSS estimate
`weighted by a quality factor adjusted by the power
`commands, wherein the quality factor decreases as a
`number of time slots between the first and second time
`slots increases, and
`means for determining the quality factor, C., of the path
`loSS estimate based on in part a number of time slots,
`D, between the first and second time slot.
`2. The user equipment of claim 1 wherein a maximum
`time slot delay is D,
`and the determined quality factor, C.,
`is determined by
`C=1-(D-1)/D.
`
`3. The user equipment of claim 1 wherein the Setting
`means Sets the transmission power level based on in part a
`desired received power level, a closed loop factor and an
`open loop factor, the closed loop factor is based on in part
`the received power commands and the open loop factor is
`based on in part the pathloSS estimate weighted by the
`quality factor.
`4. The user equipment of claim 1 wherein the Setting
`means Sets the transmission power level based on in part a
`desired received power level at the first Station and a
`combined closed loop/open loop factor, the combined closed
`loop/open loop factor is based on in part the received power
`commands and the path loSS estimate weighted by the
`quality factor.
`5. The user equipment of claim 3 wherein the closed loop
`factor is updated for each received power command.
`6. The user equipment of claim 4 wherein the combined
`factor is updated for each received power command.
`7. The user equipment of claim 3 wherein the desired
`received power level is based on in part a target Signal to
`interference ratio and a measured interference level.
`8. The user equipment of claim 4 wherein the desired
`received power level is based on in part a target Signal to
`interference ratio and a measured interference level.
`
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`Equation 9
`Equation 10
`K(n) is the combined closed loop/open loop factor. AS
`shown, this factor includes both the closed loop and open
`loop power control aspects. Equations 4 and 5 Segregate the
`two aspects.
`Although the two above algorithms only weighted the
`open loop factor, the weighting may be applied to the closed
`loop factor or both the open and closed loop factors. Under
`certain conditions, the network operator may desire to use
`Solely open loop or Solely closed loop power control. For
`example, the operator may use Solely closed loop power
`control by Setting C. to Zero.
`FIGS. 5-10 depict graphs 118-128 illustrating the per
`formance of a combined closed-loop/open-loop power con
`trol system. These graphs 118-128 depict the results of
`Simulations comparing the performance of the ARIB pro
`posed System, a closed loop, a combined open loop/closed
`loop system using Equations 4 and 6 (scheme I) and a
`combined system using Equations 9 and 10 (scheme II). The
`Simulations were performed at the Symbol rate. A spreading
`factor of sixteen was used for both the uplink and downlink
`channels. The uplink and downlink channels are Interna
`tional Telecommunication Union (ITU) Channel model
`ITU-R M.1225, vehicular, type B). Additive noises were
`Simulated as being independent of white Gaussian noises
`with unity variance. The path loSS is estimated at the
`transmitting station 52 which is a UE 32 and in particular
`a mobile station. The BCH channel was used for the path
`loSS estimate. The path